Convert binary to 8-bit integer?

I currently have the following code:

   fid = fopen('input.txt', 'r');
  l = fread(fid, 13,'uint8=>char');

N=0;
            N(l=='a')=0;
            N(l=='b')=10;
            N(l=='c')=110;
            N(l=='d')=111;

              S = sprintf('%d', N);

              F = num2str(reshape([S,zeros(1,8-rem(length(S),8))],[],8));

              FF = bin2dec(F);

For demonstration purposes, let's say input.txt has a string of these characters: acacabcbaaacb

My code converts this string to binary (using the definitions in code), which ends up as: S = 011001100101101000011010

This works good, the trouble I have is I need to break these up into groups of 8 bits. F should be:

01100110

01011010

00011010

My current code, F =

000101

111000

110101

001010

Not sure how to fix that... Also, I need to convert that to decimal...if it were correctly grouped into 8 bits. I believe the bin2dec command will work...hopefully. I just can't get them grouped into 8 bits to do so. Please help.

I also need to then take this integer array created by this code, and decode it back to the letter string. If someone could help with code to convert the integer array back to binary, and then use the key:

a = 0

b = 10

c = 110

d = 111

To convert the binary back to acacabcbaaacb. Would I use some sort of while loop, or is there a simpler way? It must be done in order, from begining to end. The actual input.txt is 256000 characters long.

Thanks.